Musepack or MPC is an open sourcelossy audio codec, specifically optimized for transparent compression of stereo audio at bitrates of 160–180 (manual set allows bitrates up to 320) kbit/s. It was formerly known as MPEGplus, MPEG+ or MP+.

Development of MPC was initiated in 1997 by Andree Buschmann and later assumed by Frank Klemm, and as of 2004 is maintained by the Musepack Development Team (MDT) with assistance from Buschmann and Klemm. Encoders and decoders are available for Microsoft Windows, Linux and Mac OS X, and plugins for several third-party media players available from the Musepack website, licensed under the GNU Lesser General Public License (LGPL) or BSD licenses, and an extensive list of programs supporting the format.[1]

The psychoacoustic model of MPC is based on MPEG ISO model 2, but is extended by CVD (clear voice detection). The quantization algorithm of the MPC encoder performs spectral shaping of the noise, called adaptive noise shaping (ANS), in order to overcome the low frequency resolution of the polyphase quadrature filter bands.

In the past, MPC has been under suspicion of violating multiple patents (MP2, PNS, subband). According to the developers of MPC, all patented code has been removed and it is now believed to be free of patent encumbrance. However, one PNS patent application is still active,[2] and it is not trivial to know if MPC's own "noise substitution techniques" avoid its scope or not.

Musepack is mainly optimized for transparent encoding at the "--standard" preset (175-185 kbit/s). Very few optimisations have been made at lower bitrates (like 128 kbit/s). Nevertheless, various listening tests have been conducted in which Musepack has performed well at both lower and higher bitrates.[3][4]

Despite being optimized for 100% transparency at moderately high bitrates, MPC has also scored highly on many 128 kbit/s tests. In May 2004, a series of double-blind listening tests[5] (as reported on Slashdot[6]) suggested that Musepack and Ogg Vorbis (which was the 1.1 "aoTuV" fork at the time) were the two best available codecs for high-quality audio compression at bitrates around 128kbit/s, beating MP3, AAC, WMA, and ATRAC.

Musepack distributes the libmpcdec library for decoding MPC content. Various plugins have been developed, using that library, including for the XMMS player (on Unix). Asunder and Jack! The Knife allows ripping Audio CD tracks directly into Musepack files.

1.
Linux
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Linux is a Unix-like computer operating system assembled under the model of free and open-source software development and distribution. The defining component of Linux is the Linux kernel, an operating system kernel first released on September 17,1991 by Linus Torvalds, the Free Software Foundation uses the name GNU/Linux to describe the operating system, which has led to some controversy. Linux was originally developed for computers based on the Intel x86 architecture. Because of the dominance of Android on smartphones, Linux has the largest installed base of all operating systems. Linux is also the operating system on servers and other big iron systems such as mainframe computers. It is used by around 2. 3% of desktop computers, the Chromebook, which runs on Chrome OS, dominates the US K–12 education market and represents nearly 20% of the sub-$300 notebook sales in the US. Linux also runs on embedded systems – devices whose operating system is built into the firmware and is highly tailored to the system. This includes TiVo and similar DVR devices, network routers, facility automation controls, televisions, many smartphones and tablet computers run Android and other Linux derivatives. The development of Linux is one of the most prominent examples of free, the underlying source code may be used, modified and distributed‍—‌commercially or non-commercially‍—‌by anyone under the terms of its respective licenses, such as the GNU General Public License. Typically, Linux is packaged in a known as a Linux distribution for both desktop and server use. Distributions intended to run on servers may omit all graphical environments from the standard install, because Linux is freely redistributable, anyone may create a distribution for any intended use. The Unix operating system was conceived and implemented in 1969 at AT&Ts Bell Laboratories in the United States by Ken Thompson, Dennis Ritchie, Douglas McIlroy, first released in 1971, Unix was written entirely in assembly language, as was common practice at the time. Later, in a key pioneering approach in 1973, it was rewritten in the C programming language by Dennis Ritchie, the availability of a high-level language implementation of Unix made its porting to different computer platforms easier. Due to an earlier antitrust case forbidding it from entering the computer business, as a result, Unix grew quickly and became widely adopted by academic institutions and businesses. In 1984, AT&T divested itself of Bell Labs, freed of the legal obligation requiring free licensing, the GNU Project, started in 1983 by Richard Stallman, has the goal of creating a complete Unix-compatible software system composed entirely of free software. Later, in 1985, Stallman started the Free Software Foundation, by the early 1990s, many of the programs required in an operating system were completed, although low-level elements such as device drivers, daemons, and the kernel were stalled and incomplete. Linus Torvalds has stated that if the GNU kernel had been available at the time, although not released until 1992 due to legal complications, development of 386BSD, from which NetBSD, OpenBSD and FreeBSD descended, predated that of Linux. Torvalds has also stated that if 386BSD had been available at the time, although the complete source code of MINIX was freely available, the licensing terms prevented it from being free software until the licensing changed in April 2000

2.
Symbian
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Symbian is a discontinued mobile operating system and computing platform designed for smartphones. Symbian was originally developed as a closed-source OS for PDAs in 1998 by Symbian Ltd, Symbian OS was a descendant of Psions EPOC, and runs exclusively on ARM processors, although an unreleased x86 port existed. Symbian was used by major mobile phone brands, like Samsung, Motorola, Sony Ericsson. Symbian OS was essentially a system and required an additional user interface to form a complete operating system. Symbian OS became prominent from the S60 platform built by Nokia, first released in 2002, Symbian eventually became the most widely used smart mobile operating system. UIQ was another Symbian user interface used by Motorola and Sony Ericsson. Applications of these interfaces were not compatible with other, despite each being built atop Symbian OS. Nokia was the majority shareholder in Symbian Ltd. and purchased the entire share in 2008, the non-profit Symbian Foundation was then created to make a royalty-free successor to Symbian OS - seeking to unify the platform, S60 became the Foundations favoured UI and UIQ stopped development. Symbian^1 was created as a result in 2009, Symbian^2 was only used by carrier NTT DoCoMo, one of the members of the Foundation, for the Japanese market. Symbian^3 was released as in 2010, by time it became fully open source. Symbian^3 received the Anna and Belle updates in 2011, the Symbian Foundation disintegrated in late 2010 and Nokia took back control of the OS development. Two months later, Nokia moved the OS to closed licensing, and later outsourced Symbian development to Accenture. Although support was promised until 2016, there was little development from Accenture, in January 2014, Nokia stopped accepting new or changed Symbian software from developers. The Nokia 808 PureView was officially the last Symbian smartphone from Nokia, however NTT DoCoMo continued releasing OPP devices in Japan, which still act as middleware on top of Symbian. Phones running this include the F-07F（Japanese：--） from Fujitsu and SH-07F（Japanese：--） from Sharp in 2014, Symbian originated from EPOC32, an operating system created by Psion in the 1990s. In June 1998, Psion Software became Symbian Ltd. a major joint venture between Psion and phone manufacturers Ericsson, Motorola, and Nokia, afterwards, different software platforms were created for Symbian, backed by different groups of mobile phone manufacturers. They include S60, UIQ and MOAP, with no major competition in the smartphone OS then, Symbian reached as high as 67% of the global smartphone market share in 2006. All of this discouraged third-party developers, and served to cause the native app ecosystem for Symbian not to evolve to a scale later reached by Apples App Store or Androids Google Play

3.
Unix
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Among these is Apples macOS, which is the Unix version with the largest installed base as of 2014. Many Unix-like operating systems have arisen over the years, of which Linux is the most popular, Unix was originally meant to be a convenient platform for programmers developing software to be run on it and on other systems, rather than for non-programmer users. The system grew larger as the system started spreading in academic circles, as users added their own tools to the system. Unix was designed to be portable, multi-tasking and multi-user in a time-sharing configuration and these concepts are collectively known as the Unix philosophy. By the early 1980s users began seeing Unix as a universal operating system. Under Unix, the system consists of many utilities along with the master control program. To mediate such access, the kernel has special rights, reflected in the division between user space and kernel space, the microkernel concept was introduced in an effort to reverse the trend towards larger kernels and return to a system in which most tasks were completed by smaller utilities. In an era when a standard computer consisted of a disk for storage and a data terminal for input and output. However, modern systems include networking and other new devices, as graphical user interfaces developed, the file model proved inadequate to the task of handling asynchronous events such as those generated by a mouse. In the 1980s, non-blocking I/O and the set of inter-process communication mechanisms were augmented with Unix domain sockets, shared memory, message queues, and semaphores. In microkernel implementations, functions such as network protocols could be moved out of the kernel, Multics introduced many innovations, but had many problems. Frustrated by the size and complexity of Multics but not by the aims and their last researchers to leave Multics, Ken Thompson, Dennis Ritchie, M. D. McIlroy, and J. F. Ossanna, decided to redo the work on a much smaller scale. The name Unics, a pun on Multics, was suggested for the project in 1970. Peter H. Salus credits Peter Neumann with the pun, while Brian Kernighan claims the coining for himself, in 1972, Unix was rewritten in the C programming language. Bell Labs produced several versions of Unix that are referred to as Research Unix. In 1975, the first source license for UNIX was sold to faculty at the University of Illinois Department of Computer Science, UIUC graduate student Greg Chesson was instrumental in negotiating the terms of this license. During the late 1970s and early 1980s, the influence of Unix in academic circles led to adoption of Unix by commercial startups, including Sequent, HP-UX, Solaris, AIX. In the late 1980s, AT&T Unix System Laboratories and Sun Microsystems developed System V Release 4, in the 1990s, Unix-like systems grew in popularity as Linux and BSD distributions were developed through collaboration by a worldwide network of programmers

4.
Multimedia
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Multimedia is content that uses a combination of different content forms such as text, audio, images, animations, video and interactive content. Multimedia contrasts with media that use only rudimentary computer displays such as text-only or traditional forms of printed or hand-produced material, Multimedia devices are electronic media devices used to store and experience multimedia content. Multimedia is distinguished from mixed media in art, for example. The term rich media is synonymous with interactive multimedia, the term multimedia was coined by singer and artist Bob Goldstein to promote the July 1966 opening of his LightWorks at LOursin show at Southampton, Long Island. Goldstein was perhaps aware of an American artist named Dick Higgins, two years later, in 1968, the term multimedia was re-appropriated to describe the work of a political consultant, David Sawyer, the husband of Iris Sawyer—one of Goldsteins producers at LOursin. In the intervening forty years, the word has taken on different meanings, in the late 1970s, the term referred to presentations consisting of multi-projector slide shows timed to an audio track. However, by the 1990s multimedia took on its current meaning, in the 1993 first edition of Multimedia, Making It Work, Tay Vaughan declared Multimedia is any combination of text, graphic art, sound, animation, and video that is delivered by computer. When you allow the user – the viewer of the project – to control what, when you provide a structure of linked elements through which the user can navigate, interactive multimedia becomes hypermedia. The German language society Gesellschaft für deutsche Sprache recognized the words significance, the institute summed up its rationale by stating has become a central word in the wonderful new media world. In common usage, multimedia refers to an electronically delivered combination of media including video, still images, audio, much of the content on the web today falls within this definition as understood by millions. That era saw also a boost in the production of educational multimedia CD-ROMs, the term video, if not used exclusively to describe motion photography, is ambiguous in multimedia terminology. Video is often used to describe the format, delivery format. Multiple forms of content are often not considered modern forms of presentation such as audio or video. Likewise, single forms of content with single methods of information processing are often called multimedia. Performing arts may also be considered multimedia considering that performers and props are multiple forms of content and media. Multimedia presentations may be viewed by person on stage, projected, transmitted, a broadcast may be a live or recorded multimedia presentation. Broadcasts and recordings can be analog or digital electronic media technology. Digital online multimedia may be downloaded or streamed, streaming multimedia may be live or on-demand

5.
IPod
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The iPod is a line of portable media players and multi-purpose pocket computers designed and marketed by Apple Inc. The first version was released on October 23,2001, about 8½ months after iTunes was released, the most recent iPod redesigns were announced on July 15,2015. There are three current versions of the iPod, the ultra-compact iPod Shuffle, the compact iPod Nano, like other digital music players, iPods can serve as external data storage devices. Storage capacity varies by model, ranging from 2 GB for the iPod Shuffle to 128 GB for the iPod Touch. Before the release of iOS5, the branding was used for the media player included with the iPhone and iPad. As of iOS5, separate apps named Music and Videos are standardized across all iOS-powered products, while the iPhone and iPad have essentially the same media player capabilities as the iPod line, they are generally treated as separate products. During the middle of 2010, iPhone sales overtook those of the iPod, in mid-2015, a new model of the iPod Touch was announced by Apple, and was officially released on the Apple store on July 15,2015. The sixth generation iPod Touch includes a variety of spec improvements such as the upgraded A8 processor. The core is over 5 times faster than models and is built to be roughly on par with the iPhone 5S. It is available in 5 different colors, Space grey, pink, gold, silver, though the iPod was released in 2001, its price and Mac-only compatibility caused sales to be relatively slow until 2004. The iPod line came from Apples digital hub category, when the company began creating software for the market of personal digital devices. The aesthetic was inspired by the 1958 Braun T3 transistor radio designed by Dieter Rams, the product was developed in less than one year and unveiled on October 23,2001. Jobs announced it as a Mac-compatible product with a 5 GB hard drive that put 1,000 songs in your pocket, Apple did not develop the iPod software entirely in-house, instead using PortalPlayers reference platform based on two ARM cores. The platform had rudimentary software running on a commercial microkernel embedded operating system, portalPlayer had previously been working on an IBM-branded MP3 player with Bluetooth headphones. Apple contracted another company, Pixo, to design and implement the user interface under the direct supervision of Steve Jobs. As development progressed, Apple continued to refine the softwares look, starting with the iPod Mini, the Chicago font was replaced with Espy Sans. Later iPods switched fonts again to Podium Sans—a font similar to Apples corporate font, color display iPods then adopted some Mac OS X themes like Aqua progress bars, and brushed metal meant to evoke a combination lock. In 2006 Apple presented an edition for iPod 5G of Irish rock band U2

6.
Open-source model
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Open-source software may be developed in a collaborative public manner. According to scientists who studied it, open-source software is a prominent example of open collaboration, a 2008 report by the Standish Group states that adoption of open-source software models has resulted in savings of about $60 billion per year to consumers. In the early days of computing, programmers and developers shared software in order to learn from each other, eventually the open source notion moved to the way side of commercialization of software in the years 1970-1980. In 1997, Eric Raymond published The Cathedral and the Bazaar and this source code subsequently became the basis behind SeaMonkey, Mozilla Firefox, Thunderbird and KompoZer. Netscapes act prompted Raymond and others to look into how to bring the Free Software Foundations free software ideas, the new term they chose was open source, which was soon adopted by Bruce Perens, publisher Tim OReilly, Linus Torvalds, and others. The Open Source Initiative was founded in February 1998 to encourage use of the new term, a Microsoft executive publicly stated in 2001 that open source is an intellectual property destroyer. I cant imagine something that could be worse than this for the software business, IBM, Oracle, Google and State Farm are just a few of the companies with a serious public stake in todays competitive open-source market. There has been a significant shift in the corporate philosophy concerning the development of FOSS, the free software movement was launched in 1983. In 1998, a group of individuals advocated that the free software should be replaced by open-source software as an expression which is less ambiguous. Software developers may want to publish their software with an open-source license, the Open Source Definition, notably, presents an open-source philosophy, and further defines the terms of usage, modification and redistribution of open-source software. Software licenses grant rights to users which would otherwise be reserved by law to the copyright holder. Several open-source software licenses have qualified within the boundaries of the Open Source Definition, the open source label came out of a strategy session held on April 7,1998 in Palo Alto in reaction to Netscapes January 1998 announcement of a source code release for Navigator. They used the opportunity before the release of Navigators source code to clarify a potential confusion caused by the ambiguity of the free in English. Many people claimed that the birth of the Internet, since 1969, started the open source movement, the Free Software Foundation, started in 1985, intended the word free to mean freedom to distribute and not freedom from cost. Since a great deal of free software already was free of charge, such software became associated with zero cost. The Open Source Initiative was formed in February 1998 by Eric Raymond and they sought to bring a higher profile to the practical benefits of freely available source code, and they wanted to bring major software businesses and other high-tech industries into open source. Perens attempted to open source as a service mark for the OSI. The Open Source Initiatives definition is recognized by governments internationally as the standard or de facto definition, OSI uses The Open Source Definition to determine whether it considers a software license open source

7.
MacOS
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Within the market of desktop, laptop and home computers, and by web usage, it is the second most widely used desktop OS after Microsoft Windows. Launched in 2001 as Mac OS X, the series is the latest in the family of Macintosh operating systems, Mac OS X succeeded classic Mac OS, which was introduced in 1984, and the final release of which was Mac OS9 in 1999. An initial, early version of the system, Mac OS X Server 1.0, was released in 1999, the first desktop version, Mac OS X10.0, followed in March 2001. In 2012, Apple rebranded Mac OS X to OS X. Releases were code named after big cats from the release up until OS X10.8 Mountain Lion. Beginning in 2013 with OS X10.9 Mavericks, releases have been named after landmarks in California, in 2016, Apple rebranded OS X to macOS, adopting the nomenclature that it uses for their other operating systems, iOS, watchOS, and tvOS. The latest version of macOS is macOS10.12 Sierra, macOS is based on technologies developed at NeXT between 1985 and 1997, when Apple acquired the company. The X in Mac OS X and OS X is pronounced ten, macOS shares its Unix-based core, named Darwin, and many of its frameworks with iOS, tvOS and watchOS. A heavily modified version of Mac OS X10.4 Tiger was used for the first-generation Apple TV, Apple also used to have a separate line of releases of Mac OS X designed for servers. Beginning with Mac OS X10.7 Lion, the functions were made available as a separate package on the Mac App Store. Releases of Mac OS X from 1999 to 2005 can run only on the PowerPC-based Macs from the time period, Mac OS X10.5 Leopard was released as a Universal binary, meaning the installer disc supported both Intel and PowerPC processors. In 2009, Apple released Mac OS X10.6 Snow Leopard, in 2011, Apple released Mac OS X10.7 Lion, which no longer supported 32-bit Intel processors and also did not include Rosetta. All versions of the system released since then run exclusively on 64-bit Intel CPUs, the heritage of what would become macOS had originated at NeXT, a company founded by Steve Jobs following his departure from Apple in 1985. There, the Unix-like NeXTSTEP operating system was developed, and then launched in 1989 and its graphical user interface was built on top of an object-oriented GUI toolkit using the Objective-C programming language. This led Apple to purchase NeXT in 1996, allowing NeXTSTEP, then called OPENSTEP, previous Macintosh operating systems were named using Arabic numerals, e. g. Mac OS8 and Mac OS9. The letter X in Mac OS Xs name refers to the number 10 and it is therefore correctly pronounced ten /ˈtɛn/ in this context. However, a common mispronunciation is X /ˈɛks/, consumer releases of Mac OS X included more backward compatibility. Mac OS applications could be rewritten to run natively via the Carbon API, the consumer version of Mac OS X was launched in 2001 with Mac OS X10.0. Reviews were variable, with praise for its sophisticated, glossy Aqua interface

8.
International Organization for Standardization
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The International Organization for Standardization is an international standard-setting body composed of representatives from various national standards organizations. Founded on 23 February 1947, the organization promotes worldwide proprietary and it is headquartered in Geneva, Switzerland, and as of March 2017 works in 162 countries. It was one of the first organizations granted general consultative status with the United Nations Economic, ISO, the International Organization for Standardization, is an independent, non-governmental organization, the members of which are the standards organizations of the 162 member countries. It is the worlds largest developer of international standards and facilitates world trade by providing common standards between nations. Nearly twenty thousand standards have been set covering everything from manufactured products and technology to food safety, use of the standards aids in the creation of products and services that are safe, reliable and of good quality. The standards help businesses increase productivity while minimizing errors and waste, by enabling products from different markets to be directly compared, they facilitate companies in entering new markets and assist in the development of global trade on a fair basis. The standards also serve to safeguard consumers and the end-users of products and services, the three official languages of the ISO are English, French, and Russian. The name of the organization in French is Organisation internationale de normalisation, according to the ISO, as its name in different languages would have different abbreviations, the organization adopted ISO as its abbreviated name in reference to the Greek word isos. However, during the meetings of the new organization, this Greek word was not invoked. Both the name ISO and the logo are registered trademarks, the organization today known as ISO began in 1926 as the International Federation of the National Standardizing Associations. ISO is an organization whose members are recognized authorities on standards. Members meet annually at a General Assembly to discuss ISOs strategic objectives, the organization is coordinated by a Central Secretariat based in Geneva. A Council with a membership of 20 member bodies provides guidance and governance. The Technical Management Board is responsible for over 250 technical committees, ISO has formed joint committees with the International Electrotechnical Commission to develop standards and terminology in the areas of electrical and electronic related technologies. Information technology ISO/IEC Joint Technical Committee 1 was created in 1987 to evelop, maintain, ISO has three membership categories, Member bodies are national bodies considered the most representative standards body in each country. These are the members of ISO that have voting rights. Correspondent members are countries that do not have their own standards organization and these members are informed about ISOs work, but do not participate in standards promulgation. Subscriber members are countries with small economies and they pay reduced membership fees, but can follow the development of standards

9.
Data compression
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In signal processing, data compression, source coding, or bit-rate reduction involves encoding information using fewer bits than the original representation. Compression can be lossy or lossless. Lossless compression reduces bits by identifying and eliminating statistical redundancy, no information is lost in lossless compression. Lossy compression reduces bits by removing unnecessary or less important information, the process of reducing the size of a data file is referred to as data compression. In the context of data transmission, it is called coding in opposition to channel coding. Compression is useful because it reduces resources required to store and transmit data, computational resources are consumed in the compression process and, usually, in the reversal of the process. Data compression is subject to a space–time complexity trade-off, Lossless data compression algorithms usually exploit statistical redundancy to represent data without losing any information, so that the process is reversible. Lossless compression is possible because most real-world data exhibits statistical redundancy, for example, an image may have areas of color that do not change over several pixels, instead of coding red pixel, red pixel. The data may be encoded as 279 red pixels and this is a basic example of run-length encoding, there are many schemes to reduce file size by eliminating redundancy. The Lempel–Ziv compression methods are among the most popular algorithms for lossless storage, DEFLATE is a variation on LZ optimized for decompression speed and compression ratio, but compression can be slow. DEFLATE is used in PKZIP, Gzip, and PNG, LZW is used in GIF images. LZ methods use a table-based compression model where table entries are substituted for repeated strings of data, for most LZ methods, this table is generated dynamically from earlier data in the input. The table itself is often Huffman encoded, current LZ-based coding schemes that perform well are Brotli and LZX. LZX is used in Microsofts CAB format, the best modern lossless compressors use probabilistic models, such as prediction by partial matching. The Burrows–Wheeler transform can also be viewed as a form of statistical modelling. The basic task of grammar-based codes is constructing a context-free grammar deriving a single string, sequitur and Re-Pair are practical grammar compression algorithms for which software is publicly available. In a further refinement of the use of probabilistic modelling. Arithmetic coding is a more modern coding technique that uses the mathematical calculations of a machine to produce a string of encoded bits from a series of input data symbols

10.
High fidelity
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Ideally, high-fidelity equipment has inaudible noise and distortion, and a flat frequency response within the intended frequency range. Bell Laboratories began experimenting with a range of recording techniques in the early 1930s. Performances by Leopold Stokowski and the Philadelphia Orchestra were recorded in 1931 and 1932 using telephone lines between the Academy of Music in Philadelphia and the Bell labs in New Jersey. Some multitrack recordings were made on sound film, which led to new advances used primarily by MGM. RCA Victor began recording performances by several orchestras using optical sound around 1941, during the 1930s, Avery Fisher, an amateur violinist, began experimenting with audio design and acoustics. He wanted to make a radio that would sound like he was listening to a live orchestra—that would achieve high fidelity to the original sound. After World War II, Harry F. Olson conducted an experiment whereby test subjects listened to a live orchestra through a variable acoustic filter. The results proved that listeners preferred high fidelity reproduction, once the noise, the advent of the 33⅓ rpm Long Play microgroove vinyl record, with lower surface noise and quantitatively specified equalization curves as well as noise-reduction and dynamic range systems. Classical music fans, who were leaders in the audio market, quickly adopted LPs because, unlike with older records. FM radio, with wider bandwidth and less susceptibility to signal interference and fading than AM radio. Better amplifier designs, with attention to frequency response and much higher power output capability. New loudspeaker designs, including suspension, developed by Edgar Villchur. In the 1950s, audio manufacturers employed the phrase high fidelity as a term to describe records. Audiophiles paid attention to technical characteristics and bought individual components, such as turntables, radio tuners, preamplifiers. Some enthusiasts even assembled their own loudspeaker systems, in the 1950s, hi-fi became a generic term for home sound equipment, to some extent displacing phonograph and record player. Records were now played on a stereo, the consumer did not have to select and assemble individual components, or be familiar with impedance and power ratings. Purists generally avoid referring to systems as high fidelity, though some are capable of very good quality sound reproduction. Audiophiles in the 1970s and 1980s preferred to buy each component separately and that way, they could choose models of each component with the specifications that they desired

Four iPod wall chargers for North America, all made by Apple. These have FireWire (left) and USB (right three) connectors, which allow iPods to charge without a computer. The units have been miniaturized over time.

Comparison of spectrograms of audio in an uncompressed format and several lossy formats. The lossy spectrograms show bandlimiting of higher frequencies, a common technique associated with lossy audio compression.

In computer science and information theory, a Huffman code is a particular type of optimal prefix code that is commonly …

Constructing a Huffman Tree

Huffman tree generated from the exact frequencies of the text "this is an example of a huffman tree". The frequencies and codes of each character are below. Encoding the sentence with this code requires 135 bits, as opposed to 288 (or 180) bits if 36 characters of 8 (or 5) bits were used. (This assumes that the code tree structure is known to the decoder and thus does not need to be counted as part of the transmitted information.)